Greetings,
You won't be able to use these items inside The Feast, but we're adjusting Sprint so that while inside PvP content, it will be possible to use this action without consuming any TP. However, players will still be able to use these items inside Frontline just like before.
Currently, the secondary stats found on Aetherial gear aren't applied to your character while you are level synced or item level synced. In Patch 3.2, we're planning to adjust this so that the secondary stats will have an adequate amount of value matching the synced level or item level.
Along with this change, the item level 150 equipment obtainable from The Diadem will be changed to item level 160. Since the item level sync set for The Feast is 150, the item level 150 equipment from The Diadem will become too powerful. This measure has been put in place as a balance adjustment. With this adjustment, all the secondary stats from equipment higher than item level 150 will sync to an adequate value, making it possible for players to fight without worrying about certain gear being too powerful.